Efficient Solution-Processed n-Type Small-Molecule Thermoelectric Materials Achieved by Precisely Regulating Energy Level of Organic Dopants

To achieve efficient n-type doping, three dopants, 2-Cyc-DMBI-H, (2-Cyc-DMBI) 2, and (2-Cyc-DMBI-Me) 2, with precisely regulated electron-donating ability were designed and synthesized. By doping with a small-molecule 2DQTT- o -OD with high electron mobility, an unexpectedly high power factor of 33.3 μW m –1 K –2 was obtained with the new dopant (2-Cyc-DMBI-Me) 2 . Notably, with the intrinsically low lateral thermal conductivity of 0.28 W m –1 K –1, the figure of merit was determined to be 0.02 at room temperature. Thus, we have demonstrated that small molecules with high electron mobility and low-lying LUMO energy levels can achieve high doping efficiency and excellent thermoelectric properties by doping with n-type dopants featuring highly matched energy levels and excellent miscibility.